Strain-Rate Dependence of Vacancy Cluster Size in Hydrogen-Charged Martensitic Steel AISI410 under Tensile Deformation

2017 ◽  
Vol 373 ◽  
pp. 171-175 ◽  
Author(s):  
Kazuki Sugita ◽  
Yasumasa Mutou ◽  
Yasuharu Shirai
Keyword(s):  
Strain Rate ◽  
Positron Lifetime ◽  
Tensile Deformation ◽  
Martensitic Steel ◽  
Vacancy Cluster ◽  
Rate Dependence ◽  
Strain Rate Dependence ◽  
Strain Rates ◽  
Vacancy Clusters ◽  
Positron Lifetime Spectroscopy

The strain-rate dependence of vacancy cluster sizes in hydrogen-charged martensitic steel AISI410 under tensile deformation was investigated using positron lifetime spectroscopy. The vacancy-cluster sizes in hydrogen-charged samples tended to increase with decreasing strain rates during the tensile deformations. The vacancy-cluster sizes significantly correlated to the tensile elongations to fracture. It was revealed that the presence of large-sized vacancy-clusters can cause the degradation of mechanical properties and followed by brittle fracture.

The mechanical characteristics of a porcine spinal cord under static loading in vitro

2018 ◽  
Vol 23 (2) ◽  
pp. 43-51
Author(s):  
Robert Pasławski ◽  
Monika Jacyna ◽  
Krzysztof Jacyna ◽  
Adrian Janiszewski ◽  
Romuald Będziński
Keyword(s):  
Spinal Cord ◽  
Stress Relaxation ◽  
Strain Rate ◽  
Mechanical Characteristics ◽  
Young Modulus ◽  
Rate Dependence ◽  
Least Square ◽  
Strain Rate Dependence ◽  
Strain Rates

Background – In spite of a number of researchers, it is well known that mechanical behaviour of a spinal cord under loading has not yet been studied extensively enough. Methods - Specimens were loaded at various strain rates: 0.02/s and 0.002/s to 5% and 10% strain. After reaching defined strain value, samples were left at a constant strain for stress relaxation. Findings – The demonstrated tensile testing stress-strain response is a highly non-linear curve corresponding to low stiffness. In the toe region stress increases exponentially with the applied strain. The highest calculated stress value for 10% strain was 0,014 MPa (strain rate 0,02/s) and 0,008 MPa (strain rate 0,002/s). Linear approximation of the stress by the least square method allowed to derive Young modulus of the value: 39,68 kPa at strain rate 0,02/s and 31,07 kPa at strain rate 0,002/s. R squared value for both regressions was above 0,99 and confirmed a good quality of approximation. A and β coefficients were 1,5MPa and 31,3 at 0,02/s strain rates and 1,3MPa and 25,3 at 0,002/s strain rates correspondingly. Relative stress relaxation increased from 20% to 37% after 60 s. Absolute stress relaxation was from 0,4kPa to 2,4kPa, at 0,002/s strain rate by 5% maximum strain and 0,02/s strain rate by 10% respectively. Interpretation - Mechanical characteristics demonstrated a visible strain-rate dependence as stiffness was significantly increasing with an increase of strain rate. Mechanical characteristics demonstrated a visible strain-rate dependence as stiffness was significantly increasing with an increase of strain rate.

Deformation-induced vacancy-type defects in GaAs

1991 ◽  
Vol 69 (3-4) ◽  
pp. 298-306 ◽  
Author(s):  
P. Mascher ◽  
S. Dannefaer ◽  
D. Kerr
Keyword(s):  
Isothermal Annealing ◽  
Positron Lifetime ◽  
Total Concentration ◽  
Vacancy Cluster ◽  
Void Size ◽  
Shallow Trap ◽  
Vacancy Clusters ◽  
Positron Lifetime Spectroscopy ◽  
Average Size ◽  
Shallow Traps

Semi-insulating undoped GaAs was plastically deformed and then investigated by positron-lifetime spectroscopy. Strains between 0 and 40% and temperatures of deformation of 450, 500, and 600 °C were investigated, with detailed investigations carried out for the lowest temperature of deformation. Between 0 and 4% strain, a reduction of the grown-in vacancy response takes place simultaneously with a slight increase in vacancy cluster size to two or three vacancies. Between 4 and 6% strain a very substantial increase in vacancy production occurs but nearly all of these vacancies are clustered into voids with a radius of about 50 Å (1 Å = 10−10 m) and density in the order of 1013–1014 cm−3. The total concentration of vacancies necessary to produce these voids is 1017–1018 cm−3. This clearly shows that vacancies are formed upon deformation and that they are mobile at 450 °C. Upon further deformation to 20% strain, the overall defect concentration becomes so high that all positrons become trapped for which reason no absolute defect concentrations can be deduced. The dominant defect types can nevertheless be identified as voids (of average size of 20 Å), two- or three-vacancy clusters, and shallow traps. Isothermal annealing of 40% strained samples shows that heat treatment reduces the void concentration but increases the average void size, and results only in a small decrease in shallow-trap concentration. The shallow traps are likely the dislocation lines themselves and the small vacancy clusters appear to be associated with the dislocation lines.

Strain rate dependence of anisotropic compression behavior in porous iron with unidirectional pores

2010 ◽  
Vol 25 (6) ◽  
pp. 1179-1190 ◽  
Author(s):  
Masakazu Tane ◽  
Tae Kawashima ◽  
Hiroyuku Yamada ◽  
Keitaro Horikawa ◽  
Hidetoshi Kobayashi ◽  
...  
Keyword(s):  
Strain Rate ◽  
Split Hopkinson Pressure Bar ◽  
Rate Dependence ◽  
Strain Rate Dependence ◽  
Porous Iron ◽  
Strain Rates ◽  
Compression Behavior ◽  
Plateau Stress ◽  
Orientation Direction ◽  
Stress Region

The strain rate dependence of anisotropic compression behavior in porous iron with cylindrical pores oriented in one direction was investigated. Through high strain rate (˜103 s−1) compression tests along the orientation direction of pores using the split Hopkinson pressure bar method, it was shown that the stress–strain curve exhibits a unique plateau-stress region where deformation proceeds with almost no stress increase. The appearance of the plateau-stress region is related to the buckling deformation of the iron matrix and provides superior energy absorption. However, for the middle (˜10−1 s−1) and low strain rates (˜10−4 s−1), compression along the same direction produces no such plateau region. In fact, in contrast to compression in the parallel direction, compression perpendicular to the orientation direction of pores produces no plateau-stress regions in any of the three strain rates.

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